I worked on a DVB-H receiver back in the day and we tried to speed it up by having a complete second tuner in hardware and starting the acquisition on the next stream while decoding the first one.
We reversed the direction if the user started going backwards. We talked about a third tuner to hold the previous channel if they decided to reverse direction but the cost wasn't worth it.
The whole technology was kind of a dead man walking by that point in history. iPhone killed it all.
Not really. the definition of what the 'next' stream is could easily change depending on what the last button you pressed, with the assumption that you would continue pressing that button:
* up - next stream is one more channel up
* down - next stream is one more channel down
* last/prev - next stream is the previous channel.